Try this. Lift your right foot off the ground and rotate it clockwise. Keep rotating it round and round in a circle. While doing this, lift your right hand and draw a circle in the air in the anticlockwise direction.
Did your foot falter because it inadvertently copied the motion of the hand? It happens to almost everyone. When it happened to me, I recalled how I used to have the same difficulty when I started learning to play piano. It required considerable practice to make both the hands play independently of each other.
I thought of applying an important lesson I learnt while learning touch typing, juggling balls, playing piano, etc. to this problem. The important lesson is: start slow.
It takes some time to train the brain to do what we want it to do. It is very important to start really slow. If you are not able to do it perfectly well, you need to reduce the speed further. In the initial stage accuracy is more important than speed. Accuracy is more important than comfort too. In fact, it feels very awkward initially. It appears as if the body is not willing to do what you want. Muscles feel tense. Limbs don't move smoothly. But with practice, all of these can be overcome and finally the body and the mind learns to do it naturally and effortlessly. Speed comes naturally once you can do it accurately.
While practising this, I also happened to create a visualization technique that made the problem really simple for me. Out of curiosity, I checked whether I could rotate the left hand clockwise while rotating the right hand anticlockwise. Yes, it was easy. So, while doing this I imagined a conveyer belt sandwiched between two rollers which were being rotated by my hands. So, as the left hand rotated one roller clockwise and the right hand rotated the other one anticlockwise, the conveyer belt moved down. Next, I switched from the left hand to the right foot while trying to maintain the same motion of the imaginary conveyer belt moving down. This did the trick. When I was focussed on maintaining the motion of the conveyer belt, somehow, my right foot could rotate clockwise without much difficulty. However, the motion of the leg was still not completely smooth. I could feel that the muscles were tense. But happy with the effort so far I went to have food.
After a few hours I tried again and I was magically able to do it effortlessly and naturally. That's the second important lesson I have learnt while picking up new skills: take long breaks. I am not sure what exactly happens but it appears as if our brain absorbs the new skill as much as possible during a long break. In fact sleep works wonders for such things.